Sterols and sterol esters are important raw materials both for cosmetics and pharmaceutical products and for the food industry. For example, it is known that sterols, especially vegetable representatives (xe2x80x9cphytosterolsxe2x80x9d), are incorporated in the basal membrane of the skin and pass to the skin surface through the differentiation of the skin cells. This would explain the caring and protecting effect of phytosterols in skin cosmetics. The topical application of sterols also leads to an increased skin moisture level and to an increased lipid content. This improves the desquamation behavior of the skin and reduces erythemas which may be present. Generic discussions regarding properties of certain sterols and sterol esters used in cosmetics have been published, (R. Wachter, Parf. Kosm., Vol. 75, p. 755 (1994) and R. Wachter, Cosm. Toil., Vol. 110, p. 72 (1995)).
Another important property of phytosterols and, above all, of phytosterol esters is their hypocholesterolemic effect, i.e., their ability after oral ingestion, for example as a margarine additive, to significantly reduce cholesterol levels in the blood. This property was described as long ago as 1953 (Peterson, et al., J. Nutrit. Vol. 50, p. 191 (1953)). U.S. Pat. Nos. 3,089,939 and 3,203,862, in addition to German Patent Publication No. DE 20 35 069 (Procter and Gamble), point in the same direction. The active substances are normally added to cooking oils or edible oils and are then taken up through the food. However, the quantities used are generally small and are normally below 0.5% by weight, to prevent the edible oils from clouding or the sterols from precipitating when water is added. The incorporation of sitostanol esters in margarine, butter, mayonnaise, salad creams and the like to reduce the blood cholesterol content is proposed in International Patent Publication No. WO 92/19640 (Raision). Reference is also made in this connection to German Patent Publication No. DE-A1 197 00 796 (Henkel).
The effect of sterols and sterol esters is usually associated with the rate at which the compounds are absorbed. So far as the substances available at present are concerned, there is considerable potential for improvement in this regard. Thus, there is a need in the art to accelerate the absorption of orally administered sterols and sterol esters.
Accordingly, the present invention is directed to orally administered sterols and sterol esters in new forms having accelerated absorption. The present invention relates to the use of nanoscale sterols and/or sterol esters with particle diameters of 10 to 300 nm as food additives and as active substances for the production of hypocholesterolemic agents.
It has surprisingly been found that the absorption and hypocholesterolemic effect of sterols and sterol esters, particularly those based on vegetable raw materials, can be significantly increased if they are present in the form of nanoparticles, i.e. particles with a mean diameter of 10 to 300 and preferably 50 to 150 nm. There are two embodiments, namely the direct incorporation of the nanoparticles in the foods and the encapsulation of the particles for separate oral ingestion. The invention also includes the observation that the nanoscale sterols and sterol esters have improved solubility or dispersibility so that even larger quantities can now be clearly and permanently incorporated, for example in edible oils.
Sterols (also known as stenols) are animal or vegetable steroids which only contain a hydroxyl group but no other functional groups at C-3. In general, sterols contain 27 to 30 carbon atoms and one double bond in the 5/6 position and occasionally in the 7/8, 8/9 or other positions. Besides these unsaturated species, other sterols are the saturated compounds obtainable by hydrogenation which are known as stanols and which are also encompassed by the present invention. One example of a suitable animal sterol is cholesterol. Typical examples of suitable phytosterols, which are preferred from the applicational point of view, are ergosterols, campesterols, stigmasterols, brassicasterols and, preferably, sitosterols or sitostanols and, more particularly, xcex2-sitosterols or xcex2-sitostanols. Besides the phytosterols mentioned, their esters are preferably used. The acid component of the ester may go back to carboxylic acids corresponding to formula (I):
R1COxe2x80x94OHxe2x80x83xe2x80x83(I)
in which R1CO is an aliphatic, linear or branched acyl group containing 2 to 22 carbon atoms and 0 and/or 1, 2 or 3 double bonds. Typical examples are acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, 2-ethyl hexanoic acid, capric acid, lauric acid, isotridecanoic acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, petroselic acid, linoleic acid, conjugated linoleic acid (CLA), linolenic acid, elaeosteric acid, arachic acid, gadoleic acid, behenic acid and erucic acid and the technical mixtures thereof obtained, for example, in the pressure hydrolysis of natural fats and oils, in the reduction of aldehydes from Roelen""s oxosynthesis or as monomer fraction in the dimerization of unsaturated fatty acids. Technical fatty acids containing 12 to 18 carbon atoms, for example cocofatty acid, palm oil fatty acid, palm kernel oil fatty acid or tallow fatty acid, are preferred. It is particularly preferred to use esters of xcex2-sitosterol or xcex2-sitostanol with fatty acids containing 12 to 18 carbon atoms. These esters may be prepared both by direct esterification of the phytosterols with the fatty acids or by transesterification with fatty acid lower alkyl esters or triglycerides in the presence of suitable catalysts, for example sodium ethylate or, more particularly, enzymes, such as is described in European Patent Publication No. EP-A2 0195311 (Yoshikawa).
Production of nanoparticles
One process for the production of nanoparticles by rapid expansion of supercritical solutions (RESS) is known from the article by S. Chihlar, M. Txc3xcirk and K. Schaber in Proceedings World Congress on Particle Technology 3, Brighton, 1998. To prevent the nanoparticles from agglomerating, it is advisable to add the nanoparticles either immediately after production of the foods or to dissolve the starting materials in the presence of suitable, i.e. above all toxicologically safe, protective colloids or emulsifiers and/or to expand the critical solutions into aqueous and/or alcoholic solutions of the protective colloids or emulsifiers which may in turn contain redissolved emulsifiers and/or protective colloids. Suitable protective colloids are, for example, gelatine, chitosan, casein, gum arabic, lysalbinic acid, starch and polymers, such as polyvinyl alcohols, polyvinyl pyrrolidones, polyalkylene glycols and polyacrylates. Accordingly, the nanoscale sterols and/or sterol esters preferably used are those which are surrounded by a toxicologically safe protective colloid and/or an emulsifier. Gelatine, chitosan or mixtures thereof are preferably used. The protective colloids or emulsifiers are normally used in quantities of 0.1 to 20% by weight and preferably in quantities of 5 to 15% by weight, based on the sterols or sterol esters. Another suitable process for the production of nanoscale particles is the evaporation technique. Here, the starting materials are first dissolved in a suitable organic solvent (for example alkanes, vegetable oils, ethers, esters, ketones, acetals and the like). The resulting solutions are then introduced into water or another non-solvent, optionally in the presence of a surface-active compound dissolved therein, in such a way that the nanoparticles are precipitated by the homogenization of the two immiscible solvents, the organic solvent preferably evaporating. O/w emulsions or o/w microemulsions may be used instead of an aqueous solution. The emulsifiers and protective colloids mentioned at the beginning may be used as the surface-active compounds. Another method for the production of nanoparticles is the so-called GAS process (gas anti-solvent recrystallization). This process uses a highly compressed gas or supercritical fluid (for example carbon dioxide) as non-solvent for the crystallization of dissolved substances. The compressed gas phase is introduced into the primary solution of the starting materials and absorbed therein so that there is an increase in the liquid volume and a reduction in solubility and fine particles are precipitated. The PCA process (precipitation with a compressed fluid anti-solvent) is equally suitable. In this process, the primary solution of the starting materials is introduced into a supercritical fluid which results in the formation of very fine droplets in which diffusion processes take place so that very fine particles are precipitated. In the PGSS process (particles from gas saturated solutions), the starting materials are melted by the introduction of gas under pressure (for example carbon dioxide or propane). Temperature and pressure reach near- or super-critical conditions. The gas phase dissolves in the solid and lowers the melting temperature, the viscosity and the surface tension. On expansion through a nozzle, very fine particles are formed as a result of cooling effects.
The particular fineness of the particles promotes more rapid absorption by the blood serum after oral ingestion by comparison with conventional sterols and sterol esters. Besides the in situ encapsulation of the nanoparticles, the substances may also be dissolved or dispersed in normal foods such as, for example, butter, margarine, diet foods, frying oils, edible oils, mayonnaises, salad dressings, cocoa products, sausage and the like. The quantity in which the nanoscale compounds are used is normally of the order of 0.01 to 5% by weight, preferably between 0.1 and 2% by weight and more preferably from 0.5 to 1% by weight, based on the food.
The present invention will now be illustrated in more detail by reference to the following specific, non-limiting examples.